piece. Therefore we designed it in two hemispheres, separated by an 

 equatorial joint: this division in no way diminished the strength of the 

 whole thing, the stresses along the joint being everywhere perpen- 

 dicular to its surface. It was naturally essential that the two surfaces 

 to be joined should be perfectly flat, so that the stresses should be 

 distributed uniformly over the whole contact surface. The two hemi- 

 spheres were finished on a lathe, internally and externally, so that their 

 thickness might be uniform. At the moment of casting, each hemisphere 

 had a weight of lo tons, a 'weight that machining reduced to 5 tons. 

 The object of this process is to eliminate doubtful parts of the casting 

 which are found, generally, on the surface and upper parts of a casting. 



THE WINDOWS 



From a bathyscaphe, it goes without saying, there must be a wide 

 view of the submarine world. The cabin must be furnished with good 

 windows, without which the bathyscaphe itself would have no reason 

 for existence. 



Here we encountered a new and exciting problem. As theory is 

 completely lacking, we had to depend entirely upon experiments with 

 models. The concern with which we watched these experiments can 

 be imagined and likewise the joy we felt as we saw the ideal solution 

 appear little by little : it was only after having found it that I was able to 

 decide to go on to the construction of my submarine. 



Professor Beebe and Engineer Barton had equipped their bathy- 

 sphere with windows in fused quartz. But even with small differences 

 in pressure the results had not been satisfactory. 



In the laboratories specializing in the study of high pressures, we 

 had recourse to very tiny peepholes made of a cone in diamond. At 

 the highest pressures even these diamonds cracked regularly: it is 

 true that they were subjected to enormous pressures, about a 

 hundred times as great as those to which the windows would be 

 subjected in the sea. 



But why not simply take glass, as I had done for the stratospheric 

 balloon.^ It is because the pressures we had to resist were infinitely 

 greater. 



If a cylindrical hole bored in a plane sheet of steel is covered over 

 externally by a sheet of flat glass, a porthole is obtained which will 

 quite well resist all the pressures we were thinking of; but the diameter 

 of the opening would be too small, so that the visual field would be too 



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